Lamp



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Original Filed Oct.

July 22 1924.

Patented .lilly 22, i924.

lllll ,naar

LAMP.

Application filed Gotober 18, 1920, Serial No. 417,736. Renewed October 2S, 1921. Serial No. 511,147.

T 0 all whom 'it may concern:

Be it known that l, lVILLrAM H. VOOD, a citizen of the United States, residing at South Euclid, in the county of Cuyahoga and State of Chio, have invented a certain new and useful improvement in Lamps, of which the following is a full, clear, and exact description, reference being hadto the accompanying drawings.

This invention relates to lamps and has especial reference to those which are ernployed on automobiles, as headlights and spot lights, but is applicable to all situations in which a concentrated beam of light is desired, with a minimum of stray rays or side glare. The objects of the invention are the provision of asimple, inexpensive and one piece reflector which shall be so balanced relatively to the shape of the light source as to yield a concentrated beam within ordinary operating limits and with a minimum of side glare; the provision of a. generally parabolic reflector having portions arranged to compensate for the necessary lateral spread of the light source, especially that encountered when a V shaped filament is used; the provision of a reflector which shall permit a V shaped filament to be used in a vertical position as well as horizontally; while other objects and advantages of the invention will become apparent the description proceeds.

It is well known that a perfectly parabolic reflector will cast foward in a single parallel beam all rays which fall thereon from a source located exactly at the focal point, but such a source is absolutely unknown, all practical sources having a material size which causes all rays arising from points displaced from the focal point to stray from the principal beam.l It is Well known that v all rays arising on the parabolic axis in front of the focal point are converged, no matter upon what part of the reflector they may fall, and, conversely, that all rays arising on that axis in the rear of the focal point are diverged, no matter on what part of the reflector they may fall. It can also be demonstrated that any displacement of the light source laterally of the axis produces a displacement of the reflected rays which is similar or opposite to the direction of shift of the source depending upon whether the rays are reflected in front of or behind the parameter; rays reflected in front of the parameter accompanying and those reflected from behind the parameter reversing the lateral displacement of the source.

So far as concerns the compensation for an excessl in size of the light source in an axial direction the accepted method is the employment of a source inclined to that axis and passing through the focal point, as set forth in my earlier Patent No. 1,284,019, dated Nov. 5, 1918. This is effected practically by the combination of two (or more) such inclined sections into a V (or series of the same having a common apex) the apex being at thefocal point. This, however, entails a disadvantage in respect of the displacement of the extremities of the filament laterally of the axis; and any attempt to compensate the same which is effective so far as concerns one side of the parameter only intensifies the effect produced at the other side of the parameter.

The adoption of the V shaped filament led to an immediate and great reduction in the depth of the reflector bowl so as to reduce to its smallest extent the portion` infront of the parameter; a second step was an increase in the width of the lens holding ring to over hang the forward portion of the reflector and catch the glaring rays. It is not feasible to terminate the reflector at the parameter sincethis would not leave room inside the lens for a lamp bulb, unless the glass be bowed or unless an unsightly gap be left between the reflector and the glass, though both these expedients have been tried. Both of these offer the disadvantage of losing an undue amount of light in the form of direct rays, and the former has the further disadvantage that the bowed glass is expensive.

The essence of my invention consists in terminating the main parabolic surface at or near its parameter and continuing the reflector in front of that plane by a second parabolic surface so related to the li htsource as to concentrate instead of diffusing it throughout the operating range.

1n the drawings accompanying and forming a part of this application, I have illustrated one embodiment of my invention to-A gether with various diagrammatic views showing the theory thereof. Fig. 1 is a sectional view through a spot-light embodying my improvements, the different parts bein@ exaggerated; Figs. 2 and 3 are horizontal and vertical sectional views drawn to scale and showin the base portion of the component para oloids; Figs. 4 and 5 are similar views showing the mouth portion of said paraboloids; Fig. 6 is a diagrammatic view showing the relations of the two paraboloids in the finished reflector; Fig. 7 is a front View of the reflector drawn to smaller scale, and Fig. 8 illustrates my improvements as applied to a preferred form of headlight.

My improved reflector comprises a paraboloid portion A extending substantially to the plane of its parameter and merging at that oint with a second paraboloid portion which is preferably coaxial therewith (although not always, especially when it constitutes less than a complete circumference) and preferably or generally has its focal point located rearwardly of the focal point of the first paraboloid as a result of displacement, inclination or size. It will be convenient to consider the light source in its relation to the different paraboloid portions independently of each other, first referring to Figs. 2 and 3 which show the portion A. The parabolic axis being indicated at a/- and the focal point at f which here coincides with the most advanced portion of the source S (here shown as a V shaped filament), it will be clear that all rays originating at the point f and falling upon the paraboloid will be reected forwardly as shown at b parallel to the axis ufl-a, such being the essential characteristic of a paraboloid. The rays such as those shown at c, originating to the rear of this focal point tend by reason of such rearward displacement to be diverged, and by their origin at a point displaced laterally from the axis tend to become converged, these two conditions serving largely to neutralize each other and throw the rays forward parallel to the axis as indicated at c c. This, last condition holds only for such portions of the rays as fall within the parameter P-P, those falling outside of the parameter being markedly diverged as illustrated at d, but this difficulty is avoided by terminating this reflector portion either at the parameter or so near the same as to avoid any marked glare.

Referring to Figs. 4 and 5 it will be noted that the focal point of the portion B is in-Y dicated at f and is located at the rear of the source S; and only that portion of the paraboloid B is employed which lies forward of the equatorial Q--Q Whose perimeter is equal to P-P. All rays arising from thepoint of the filament are converged as shown at e by reasony of the forward displacement of that'point along the parabolic axis; all the rays arising from the rearmost part of the filament are reflected forward as shown at vg substantially parallel with the parabolic axis by reason of the fact that they come approximately from the focal Lacasse point itself; and inasmuch as no rays arise behind the focal point nor issue from that direction, those particular rays which are most fruitful in causing glare are entirely eliminated.

Upon securing these two portions together as shown in Fig. 6 with their axes coincident and their focal points overlapping with the light source included between such focal points, it will be seen that the beneficial action of each paraboloid portion is retained while the portions of such paraboloids which ordinarily producea detrimental effect are avoided. Also by Abringing the focal points as nearly together as possible any such convergence of the rays as might have a similar effect islikewise avoided.

When my improved reflector is used in a projecting lamp, as for example an automobile spot-light, the light source is set in the axis of the reflector with its foremost part coincident with the focal point of the rearmost portion as a result of which practically all the rays reflected by that portion constitute a parallel beam, while the rays reflected by the forward portion are converged. The rays originating at the forward extremity of the source are converged most, those rays which originate further back being converged a smaller amount partly by reason of their originating further back and partly by reason of their originating at one side of the axis. ln order to prevent this convergence from causing the rays to strike too abruptly across the axis and thus producing an objectionable glare it is best to have the two focal points separated only by a sufficient distance to include the source between them. in this way practically all the rays striking the reflector can be focussed on the area to be yilluminated which in a spot-light is only from twenty to one hundred feet from the lamp. This not only dispenses with the necessity of shielding the mouth portions of the reflector but also enables the reflector to be lengthened somewhat, this utilizing more of the direct rays which are generally wasted. rlhe best results are obtained with a i! shaped source but any concentrated type can be employed with good results.

When a a shaped source is used in a headlight having a plain parabolic reflector experience shows that its glare is least objectionable when it is mounted horizontally although its driving qualities are best when it is set vertically, and practically all present day headlights are constructed so that the lamps can be inserted only with the filament horizontal. By the use of my improved reflector it becomes possible to set the filament vertically or to use a double V shaped lament as shown in my copending application filed @ctober 28, 1920, Serial No. 420,074.

1,5oa45a This also enables the reiectors to be made deeper and a larger proportion of the rays employed usefully, especially in case the side wings C, C be employed as shown in my Patent No. 1,235,275 issued July 31, 1917. In this case the lower half D is inclined downwardly to prevent glare, and the portion B can constitute either a smaller paraboloid concentric with A or its glare can be overcome by inclination relative to that-axis.

It will be understood that my improved reiector can be made by actuall cutting apart two paraboloid members an securing them together at the points indicated, but in practice it is preferable, to make it of a single piece of sheet metal drawn in dies to produce the paraboloid 'portions described. This can be effected in a single operation (unless the bowl be made so deep as to necessitate a drawing in two stages), the dies are no more expensive than the simple parabolic dies, and the polishing operation can be performed in the usual way and without increased expense. The reflectors have no freakish or unusual appearance and can be distinguished from Vthe usual reflector only by careful examination.

It will be understood that I do not limit myself to the specific uses herein described, nor to the employment of any one type of light source, nor in any other Way except as set forth in the annexed claims.

Having thus described my invention, what I claim 1s:

1. An automobile headlight comprisin in combination, a one piece reflector w ose vertical section exhibits two approximately parabolic portions arranged one in front of the other, the focal point of the foremost portion being located rearwardly of that of the rearmost portion and the surfaces of the two portions merging together substantially opposite said focal points, having a V shaped light source in said reflector symmetrically arranged relatively to said axis and having its apex presented toward the open face of said reflector.

2. In an automobile headlight, la reflector Whose axial -section exhibits two approximately parabolic portions arranged one in front of the other, the focal point of the foremost portion being located rearwardly of that of the rearmost portion and the surface of the two portlons being merged physically together within the zone defined between the parameters of the two portions, in combination with a V shaped light source,

which is symmetrically arranged relatively to the common axis of said paraboloids.

3. In a lamp, a one piece reiector having twoy approximately parabolic sections one ahead of the other, the common axis o ysaid sections being substantially horizontal,

other, the focal point of the foremost section being located in the rear of the focal point of the rearmost section, and the two sections merging together substantially in that zone which is bounded by the parameters of said sections, in combination with a light source which is substantially symmetrical relatively to said axis and has its rearmost section displaced laterally from said axis.

5. In a lamp, a reector having two coaxial parabolic sections, one ahead of the other, the focal point of the foremost section being located in the rear of the focal point of the rearmost section, and the two sections merging together substantially in that zone which is bounded by the parameters of said sections, in combination with a V shaped light source whose vertex coincides substantially with the axis of such rearmost section and whose win r terminate ahead of the focal point of the foremost section.

6. In a lamp, a reflector having two coaxial parabolic sections, one ahead of the other, the focal point of the foremost section bein located in the rear of the focal point of t e rearmost section, and the two sections merging together substantially in that zone which is `bounded by the aameters of said sections, in combination with a V shaped light source Whose plane coincides substantially with such axis, whose apex coincides substantially with the focal point of the rear- .most section and whose rearmost part extends not materially beyond the parameters of the foremost section.

In testimony whereof, I hereunto atlix my signature.

WILLIAM H. WOOD. 

